1. Field of the Invention
The present invention relates to Mobile IP network technology. More particularly, the present invention relates to enabling mobility for a node that changes its location within a network through the use of control messages that are sent and received by access points.
2. Description of the Related Art
Mobile IP is a protocol which allows laptop computers or other mobile computer units (referred to as “Mobile Nodes” herein) to roam between various sub-networks at various locations—while maintaining internet and/or WAN connectivity. Without Mobile IP or related protocol, a Mobile Node would be unable to stay connected while roaming through various sub-networks. This is because the IP address required for any node to communicate over the internet is location specific. Each IP address has a field that specifies the particular sub-network on which the node resides. If a user desires to take a computer which is normally attached to one node and roam with it so that it passes through different sub-networks, it cannot use its home base IP address. As a result, a business person traveling across the country cannot merely roam with his or her computer across geographically disparate network segments or wireless nodes while remaining connected over the internet. This is not an acceptable state-of-affairs in the age of portable computational devices.
To address this problem, the Mobile IP protocol has been developed and implemented. An implementation of Mobile IP is described in RFC 2002 of the Network Working Group, C. Perkins, Ed., October 1996. Mobile IP is also described in the text “Mobile IP Unplugged” by J. Solomon, Prentice Hall. Both of these references are incorporated herein by reference in their entireties and for all purposes.
The Mobile IP process and environment are illustrated in FIG. 1. As shown there, a Mobile IP environment 2 includes the internet (or a WAN) 4 over which a Mobile Node 6 can communicate remotely via mediation by a Home Agent 8 and a Foreign Agent 10. Typically, the Home Agent and Foreign Agent are routers or other network connection devices performing appropriate Mobile IP functions as implemented by software, hardware, and/or firmware. A particular Mobile Node (e.g., a laptop computer) plugged into its home network segment connects with the internet through its designated Home Agent. When the Mobile Node roams, it communicates via the internet through an available Foreign Agent. Presumably, there are many Foreign Agents available at geographically disparate locations to allow wide spread internet connection via the Mobile IP protocol. Note that it is also possible for the Mobile Node to register directly with its Home Agent.
As shown in FIG. 1, Mobile Node 6 normally resides on (or is “based at”) a network segment 12 which allows its network entities to communicate over the internet 4 through Home Agent 8 (an appropriately configured router denoted R2). Note that Home Agent 8 need not directly connect to the internet. For example, as shown in FIG. 1, it may be connected through another router (a router R1 in this case). Router R1 may, in turn, connect one or more other routers (e.g., a router R3) with the internet.
Now, suppose that Mobile Node 6 is removed from its home base network segment 12 and roams to a remote network segment 14. Network segment 14 may include various other nodes such as a PC 16. The nodes on network segment 14 communicate with the internet through a router which doubles as Foreign Agent 10. Mobile Node 6 may identify Foreign Agent 10 through various solicitations and advertisements which form part of the Mobile IP protocol. When Mobile Node 6 engages with network segment 14, Foreign Agent 10 relays a registration request to Home Agent 8 (as indicated by the dotted line “Registration”). The Home and Foreign Agents may then negotiate the conditions of the Mobile Node's attachment to Foreign Agent 10. For example, the attachment may be limited to a period of time, such as two hours. When the negotiation is successfully completed, Home Agent 8 updates an internal “mobility binding table” which specifies the care-of address (e.g., a collocated care-of address or the Foreign Agent's IP address) in association with the identity of Mobile Node 6. Further, the Foreign Agent 10 updates an internal “visitor table” which specifies the Mobile Node address, Home Agent address, etc. In effect, the Mobile Node's home base IP address (associated with segment 12) has been shifted to the Foreign Agent's IP address (associated with segment 14).
Now, suppose that Mobile Node 6 wishes to send a message to a corresponding node 18 from its new location. An output message from the Mobile Node is then packetized and forwarded through Foreign Agent 10 over the internet 4 and to corresponding node 18 (as indicated by the dotted line “packet from MN”) according to a standard internet protocol. If corresponding node 18 wishes to send a message to Mobile Node—whether in reply to a message from the Mobile Node or for any other reason—it addresses that message to the IP address of Mobile Node 6 on sub-network 12. The packets of that message are then forwarded over the internet 4 and to router R1 and ultimately to Home Agent 8 as indicated by the dotted line (“packet to MN(1)”). From its mobility binding table, Home Agent 8 recognizes that Mobile Node 6 is no longer attached to network segment 12. It then encapsulates the packets from corresponding node 18 (which are addressed to Mobile Node 6 on network segment 12) according to a Mobile IP protocol and forwards these encapsulated packets to a “care of” address for Mobile Node 6 as shown by the dotted line (“packet to MN(2)”). The care-of address may be, for example, the IP address of Foreign Agent 10. Foreign Agent 10 then strips the encapsulation and forwards the message to Mobile Node 6 on sub-network 14. The packet forwarding mechanism implemented by the Home and Foreign Agents is often referred to as “tunneling.”
Since a node may not support Mobile IP, a node that changes its location within a network cannot initiate registration with its Home Agent. Proxy mobile IP support (i.e., proxy registration) may therefore be performed by an Access Point on behalf of the node. An Access Point (AP) is the center point in an all-wireless network or serves as a connection point between a wired and a wireless network. Multiple APs can be placed throughout a facility to give users with WLAN adapters the ability to roam freely throughout an extended area while maintaining uninterrupted access to all network resources. Once a node is registered with a Home Agent, packets may be forwarded by the Home Agent to the Foreign Agent. Moreover, the access point may also redirect packets sent by the node to the Foreign Agent, enabling the redirected packets to be sent to the appropriate destination by the Foreign Agent. application Ser. No. 10/080,995, entitled “METHODS AND APPARATUS FOR SUPPORTING PROXY MOBILE IP REGISTRATION IN A WIRELESS LOCAL AREA NETWORK,” by inventors Wang et al, filed on Feb. 20, 2002, which discloses a method of supporting proxy registration by an Access Point, is incorporated by reference for all purposes.
In order to send a registration request on behalf of the node, the Access Point needs the node's IP address and Home Agent address (i.e., default gateway) in order to compose a registration request packet. In addition, the Access Point also ascertain's the node's sub-network network mask (i.e., netmask) in order to ascertain whether Mobile IP proxy services are required. Specifically, when the Access Point determines from the source address of a data packet and the netmask that the node is located on the subnet identical to the subnet of the Access Point, no Mobile IP service is required on behalf of the node as shown at block. However, when the Access Point determines from the source address that the node is not located on the subnet of the Access Point, proxy Mobile IP service is performed by the Access Point is performed on behalf of the node.
The node typically provides its configuration information such as IP address, default gateway (e.g., Home Agent), and network mask in an IP packet such as an IP data packet sent to the initial Access Point. As the node roams to another location, it roams to another Access Point. However, this subsequent Access Point within the network is not in possession of the node's configuration information. Moreover, the node is unaware that this subsequent Access Point does not have its configuration information.
In view of the above, it would therefore be desirable to enable the subsequent Access Point to obtain this configuration information without involvement, modification or configuration of the node.